MT(MOD_RALT,KC_SPC) is saved wrong

[propri]

When you program a key with MT(MOD_RALT,KC_SPC), it is saved as MT(MOD_LALT | MOD_RALT,KC_SPC). Both with the app and the website.

[lesca]

this is the issue of the QMK not VIA.

Currently, the kc argument of MT() is limited to the Basic Keycode set, meaning you can’t use keycodes like LCTL(), KC_TILD, or anything greater than 0xFF. This is because QMK uses 16-bit keycodes, of which 3 bits are used for the function identifier, 1 bit for selecting right or left mods, and 4 bits to tell which mods are used, leaving only 8 bits for the keycode. Additionally, if at least one right-handed modifier is specified in a Mod-Tap, it will cause all modifiers specified to become right-handed, so it is not possible to mix and match the two - for example, Left Control and Right Shift would become Right Control and Right Shift.

source: https://docs.qmk.fm/#/mod_tap

[propri]

I don't quite understand how that relates to my problem? The keycode part works as expected, but the modifier doesn't. I am also not mixing any right/left modifiers.

I want to have a key that acts as space when tapped, but as RALT when held. If I try to program it with the any function of via as described above, the key acts as both RALT and LALT at the same time when held.
If I program it with LALT instead, it is saved as MT(MOD_LALT,KC_V) as expected.
Non QWERTY layouts often need to use RALT to reach certain symbols, and activating both RALT and LALT at the same time leads to unexpected and wrong inputs.

When I programmed my keyboard with QMK directly, I could achieve this by using RALT_T(KC_SPC), but VIA doesn't seem to support the RALT_T().