Short answer, I think: don't pause when remapping in mame.
More details:
MameUI is the current name of was mame32 (as it has both 32 bit and 64 builds
as does mame, and mame was 32 bit for over 5 years anyway).
WinIpac is for changing what keypresses the ipac sends to the computer. IOW, it's for configuring the ipac, and has nothing to do (directly, at least) with mame or mameUI.
Mame's tab input remap menu works as such:
- Left side is the game's input, right is what is mapped in mame to that input.
- Multiple keys or key combos can be mapped to the same game input. Example: You want "P1 Up" pressed if mame sees either the A or T key pressed, or if both the O & E keys were pressed at the same time, or "key_A or key_T or (key_O and key_E)". This would be shown as "A OR T OR O E".
- Having "Ctrl Left Ctrlr Right" on the right side means mame is looking for both the ctrl keys for mame to send the game that input.
- Having "..." means the keys that are mapped do not fit in the space given. Scolling over will expand in a box the keys that are mapped. (This is not a choice box.)
- Pressing the key mapped to UI_select (usually enter) tells mame to change to the key/keys next pressed. If you want A, press enter, press A, then wait until mame excepts the change (~ one sec). If you want A or B: enter, A, wait, enter, B. If you want A + B: enter, press A and B before the second is up, wait. To start over, scroll off the input, go back on and continue as normal.
If paused, the ctlr, alt and shift buttons (defaults or P1 B1, B2, & --BINGO! Either that, or I was attempting to say "before" but it was too many letters to type--, respectively) usually are seen as both the left & right, even if you press only one. So just don't pause while remapping.
Mame FAQ is a good place to start.