C Key in lr-MAME(Current v0.171) acting as Tab key too

ThinkerCM

Pi Model: 3
RetroPie Version: 3.7
Built From: SD Image
USB Devices connected: Keyboard and/or MiniPac
Controller used: MiniPac
Emulator: Mame (Current v0.171) Experimental

I've built my own arcade stick using a MiniPac, it works fine on my PC and works okay with lr-Mame 2003 and AdvMame 1.4 on the Pi 3 running RetroPie3.7.

I recently installed lr-Mame (Current) which is using the source code for MAME 0.107, but for some reason it considers the Enter Key to be Joy 1 Start button (this is sort of understandable as the the Enter Key is assigned to the Joy 1 Start button in EmuStation input config and I assume it's basing the key strokes on this somehow), but it also reads the C key as both the C key and the Tab key, but neither the C or Tab key are assigned to anything in EmuStation.

I'm pretty sure it's got nothing to do with both the keyboard and MiniPac being plugged in at the same time as I've tried it with both individually and get the same results.

I've been using MAME for years, back when you had to use 3 different emulators (Raine, RAGE and Callus) to play Chase HQ, R-Type and Final Fight. But I've never seen this issue before so I'm certain it's a configuration problem...

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Mid-post update
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Okay I've resolved the issue now but thought I'd post this anyway in the interests of sharing information.
I was typing this while waiting for lr-Mame(2010) to install so I could check if the same issue existed for that version (and it did) but after some fiddling I discovered the following....

I had set up the C key to be the bottom Left button on the EmuStation controller previously (but had since removed that assignment, or so I thought, via the GUI) but EmuStation had maintained the original key assignment so C = Bottom Left button.
The Bottom Left Button as assigned in EmuStation is setup by RetroArch to be the equivalent of the Tab key in Mame which is why the C key was being read as a C and Tab at the same time and hence, whenever I tried to Throw a Hard Punch in SF2 the Config Menu appeared.

So I did some digging around and did the following

Retropie Menu Screen > Configuration Editor > Advanced Configuration > Manually Edit RetroArch Configurations > all/retroarch.cfg
Scroll down and remove the # before the input_libretro_device_p1/2 lines and place a 3 after the equals sign on each line
* This will force the Player 1 and 2 controllers to be recognised as keyboards (as the MiniPac should be recognised) but I'm not really sure this is necessary
Further down you will find the line Keyboard Input, Joypad and Joyaxis will all obey...etc and beneath that the Joypad inputs that EmuStation requests you enter, I changed the L2 inputs to "nul" I also changed the R2, L3 and R3 inputs to "nul"
Now in MAME, the C key is no longer opening and closing the Config menu.

I don't know for sure, but I believe this only affects the mappings for games using RetroArch and not EmuStation itself, I need to do some more Playing before I'll know what issues it might cause elsewhere, I only got my Pi 4 days ago so I'm pretty new to this,.