I found a workaround for now: turn off continuous scrolling. (see line 5085 of View_pat.cpp).

Also, when continuous scroll is enabled and there is another pattern ahead, chord detect interval does not work as advertised:

"If you have the Pattern Editor’s Edit Step setting set to some other value than 0 and have a record group set up, OpenMPT will put all notes detected within the Chord Detect Interval on the same row, regardless of the Edit Step setting, i.e. the notes are interpreted as a chord."

The first note is placed on the row, the cursor jumps ahead by the edit step (into the next pattern), and since continuous scroll is enabled, the pattern does not jump back (in fact, it looks like the code to make the jump back, starting on line 4883, assumes the pattern did not change after placing the first note). Instead, the second note is placed in the second pattern.

Yes, it does not work as advertised because it's buggy. The problem basically is that the chord detect interval has to "undo" the pattern change; this currently not possible because it doesn't remember in which pattern the chord was started. Fixing this is probably as trivial as remembering the current pattern in which a note is entered.

Please try r12065, it should fix the issue.

It works great, thank you!
I couldn't find it on builds, so I tested with 12066 if that makes a difference.

12066 is the backport for OpenMPT 1.28 (rather than bleeding-edge 1.29) but apart from that it's the same. Good to hear that it's working.