My client embeds raster PSDs that include an additional spot channel and applies pre-distortion to them using Envelope or Effect > Warp > Arc. When the PSD is embedded, the spot channel becomes a Transparent Single Ink Image in the DeviceN color space with an alpha channel.

After applying Envelope or Warp > Arc, the spot channel percentage is multiplied by the alpha channel value, while the alpha channel itself remains in the image. The result is a significant reduction in the effective spot ink coverage.
In the attached example, a 50% spot in the original becomes 25% after the operation.

Steps to reproduce
1. Create a PSD containing a spot channel set to 50% and saved with transparency.
2. Embed the PSD into the document so the spot channel is represented as a Transparent Single Ink Image in DeviceN with an alpha channel.
3. Apply Envelope or Effect > Warp > Arc to the embedded PSD.
4. Inspect Acrobat Output Preview > Separations and compare the spot channel percentage before and after the effect.

Actual result
The spot channel percentage is multiplied by the alpha channel value during the Envelope or Warp operation, while the alpha channel remains present in the image. This reduces the visible spot ink amount. Example: 50% spot becomes 25% in the post-effect image.

Expected result
A spot channel percentage should be retained regardless of the Envelope/Arc effect applied.

Technical notes
• The embedded spot channel is exported as a Transparent Single Ink Image in DeviceN with an alpha channel.
• The problem appears to occur when geometric distortion is applied via Envelope or Effect > Warp > Arc.
• Output Preview tools such as Acrobat Output Preview > Separations can be used to verify the discrepancy.

Attachments
I have attached a PDF that demonstrates the issue and includes the separations for convenience. Please compare the spot percentages in the original image and in the images after Envelope.

Severity
High for print accuracy and color separation workflows. This leads to incorrect ink percentages on separations and can cause production color failures.