Thank you for the post.
To attempt to replicate, I performed the following steps:
1. Created a new database with 2 tables (UI & Data)
2. Created a one-to-many relationship (Pk_Data ---< fk_UI)
3. Created a portal with scroll bar showing 5 records on the UI table
4. Created 50 records in the data table and populated the portal with 50 records
5. Hosted the file with FileMaker Server 13.0v2 on a Mac OS X 10.8.5 iMac
6. Connected to the solution with WedDirect using Safari 6.1.3
7. Spent around 20 minutes clicking and dragging the scroll bar
The scroll bar always remained at the last position. I understand this only happens "sometimes," so am I missing a step to replicate?
Does this occur in a new test file or could you provide a sample file that replicates?