Column Bleeding or Leakage?

To: WENSWTo my best knowledge, this analyte (Dimethyl 1,3-acetonedicarboxylate, cas#1830-54-2) should not be a problem for you.
If the assay method is well developed and transferred, so my first comment to your question is the bleeding of the Capillary Columns. ( Column bleed is a result of stationary phase fragments releasing from the inside wall of the column. )
Here are some comments:
(1) Double check the leakage of the GC system.
(2) If NOT, change another polar capillary column: Polyethylene glycol (PEG) Polar Capillary GC Columns or high performance low bleed, highly inert, polar fused silica GC columns ->50% Cyanopropylphenyl Polysiloxane.
(3) Perform a Grob test on that previous by following the on my Tech-Notebook 2006. {(K. Grob Jr. G. Grob, and K. Grob, J. Chromatogr. 156 (1978) 517; K. Grob, G. Grob, and K. Grob Jr., J. Chromatogr. 219 (1981) 13.). } or check the weblink of Grob Test.