Reaper v4.602 x64 (and 4.61pre4), Windows 7 x64.
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This issue has now been confirmed and posted in the issue tracker:
http://forum.cockos.com/project.php?issueid=5110
Please click on the appropriate option in the issue post to confirm the bug to the developers.
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I've included a test project in the attachments that uses a 1-band ReaEQ. You'll have to roll your own presets to test this however. I use a 1-band ReaEQ on an non-automated track to make them, and then loaded them on the ReaEQ instance on the automated track.
A licecap of it can be
downloaded here (~1MB). You can play this by dropping it in to Reaper and bringing up the Video window from the View menu.
The licecap file shows that the track is in Latch mode(purple box on the left), the plugin GUI is open, the parameters are activated and armed.
I load presets, nothing changes on the envelope lanes, but the parameters do change. After I stop transport (playhead no longer moves) the values return to normal, i.e. what the envelopes show, after a few seconds of doing nothing. I repeat this with WRITE mode and READ mode. Same result.
The loading of presets does not appear to trigger a write in Latch mode at all for me, for any parameter.
Disturbingly however, the parameters do actually change, both on the GUI of the plugin (ReaEQ and DC8C2 confirmed) and on the Envelope Control Panel value indicators.
However, none of these parameters are being written to, according to the envelopes themselves which I am displaying, and the Envelope Control Panel controls which are not getting their red background, instead of the yellow, which indicates ready-to-write. Red would have been "writing".
I can actually relocate the play head and the values the preset loaded. Only if I leave Reaper be for a few seconds, do the parameters return to the values that are on the envelopes.
What is supposed to happen when Latch mode is active on a track and the talked about parameters are activated and armed :
Any change to those parameters while transport is in PLAY mode triggers a write. This goes for manual parameter changes and preset loading.
Could I get some confirmation from anyone ?