Chris Martin, on loan from Norwich, scored a 36th-minute goal which looked set to end the Eagles' five-match winless run, but they were undone midway through the second half by Scotland's impressive finish.
Ipswich would have been disappointed enough just to have fallen behind nine minutes before the break but for a player borrowed from their greatest rivals to score was a double blow.
Paul Jewell's men were arguably the better side in the first half and they gave Eagles goalkeeper Julian Speroni plenty to do.
Lee Martin's long-range drive after just three minutes was gathered uneasily by Speroni, who scampered across his goal moments later as Andy Drury's ambitious shot flew narrowly wide.
The hosts hit back with a strong run from Stuart O'Keefe but his cross was plucked out of the air by Arran Lee-Barrett.
Ipswich were quickly on the front foot again, Grant Leadbitter arrowing a shot wide from 25 yards before Jay Emmanuel-Thomas stung Speroni's palms with a strike from even further out.
Lee-Barrett went full stretch to keep out Darren Ambrose's dangerous effort midway through the half before Lee Martin saw his shot bravely blocked by Patrick McCarthy.
Speroni's one-man resistance continued in the 25th minute as Scotland's well-timed volley was parried to safety and then Emmanuel-Thomas was denied from distance.
Just as it appeared as though Ipswich were building up to something, their momentum was halted as Dougie Freedman's men took the lead.
Nathaniel Clyne linked well with Sean Scannell before delivering a low cross for Chris Martin, who fired in from 12 yards.
After an even start to the second half it was Ipswich who made the first decisive move. Leadbitter fed Scotland and he weighed up his options before unleashing a shot from outside the area which skidded into the bottom right corner.
Aaron Cresswell saw a late shot blocked by McCarthy and substitute Kyle De Silva went close for Palace but Freedman's side were forced to settle for their 11th home draw of the campaign.